Synthesis, Antioxidant and Antituberculosis Evaluation of Eugenol Derivatives from Mannich Condensation

Mannich bases are interesting class of molecules thanks to their various pharmacological properties. This paper presents the synthesis and characterization of eugenol derivatives following Mannich condensation. The in vitro antituberculosis activity of the synthesized derivatives was evaluated by the Resazurin microtiter assay (REMA). The 2,2 '-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and ferrous cation (FeCl2) chelating tests were used to estimate the antioxidant capacity. All eugenol Mannich bases inhibited the Mycobacterium tuberculosis (Mtb) H37Rv growing. Those of 2-dimethylaminomethyl-6-methoxy-4-propenylphenol (1) and 2-methoxy-4-propenyl-6-pyrrolidinylmethylphenol (4) were the most active at 10 mu g/mL. Additionally, significant antioxidant profile was exhibited by the synthesized derivatives, especially for 2-dicyclohexylaminomethyl-6-methoxy-4-propenylphenol (5) that showed an antiradical activity of EC50=20 mu g/mL, twice as strong as that of eugenol precursor, and for 2-methoxy-6-methylpiperazinylmethyl-4-propenylphenol (3) and compound 4, which were promising iron chelators with EC50 of 0.016 and 0.018 mg/mL, respectively, better than EDTA standard. The molecular docking experiments on two different antituberculosis receptors showed excellent binding affinity of compounds 4 and 5 into the active site of pantothenate kinase (PanK, type I), suggesting PanK as potential molecular target. These encouraging findings showed the importance of Mannich reaction for the development of antitubercular candidates and the improvement of natural products bioactivity.